1. Field of the Invention
The present invention relates to a bearing apparatus for permitting axial, rotational and angular movement of a doctor journal of a papermaking machine. More particularly, the present invention relates to a bearing apparatus which permits axial oscillation of a doctor in a papermaking machine.
2. Information Disclosure Statement
Doctors are used in all sections of a papermaking machine.
A doctor essentially includes a doctor back, a blade holder and an elongate blade which, when disposed in an operative disposition, cooperates with the cylindrical surface of a roll for peeling or doctoring a web therefrom.
Such doctors are used for cleaning a roll surface, removing a sheet during threading, creping a web, spreading or metering a coating onto a web and sealing a breast roll in a forming section.
In the case of a press section, a doctor typically cooperates with the surface of a press roll for doctoring the wet web therefrom.
However, when the web has been guided from the press roll into and through the subsequent drying section, the doctor blade can be moved from the operative to an inoperative disposition thereof away from the surface of the press roll while the blade is disposed substantially parallel to the rotational axis of the press roll.
Similarly, in the case of a dryer section doctor, the doctor cooperates with the heated outer surface of a drying cylinder such that the web can be doctored therefrom. However, during operation of the drying section, when the drying section has been threaded, the doctors can be moved from their respective drying cylinders to an inoperative disposition thereof.
In both press section and drying section applications, the blade of the doctor is urged into an operative disposition relative to the surface from which the web is to be doctored. Therefore, in the event of a contaminant becoming lodged between the doctor blade and the rotating surface being doctored, such contaminant tends to score the surface of the roll.
Accordingly, oscillating doctors have been proposed in which the doctor in the operative disposition thereof moves axially relative to the roll surface. Such axial movement of the doctor, or oscillation thereof, tends to dislodge any contaminant and, therefore, prevents scoring of the roll surface.
Typically, an oscillating doctor will oscillate through a stroke of approximately one-half inch.
Accordingly, it would appear that the provision of a sliding bearing at both ends of a doctor would be all that would be required, such sliding bearings permitting rotation of the doctor blade away from the roll surface to an inoperative disposition while permitting axial oscillation of the doctor during operation thereof.
However, in view of the fact that doctors typically cooperate with rolls having a width in the region of 34 feet, those skilled in the art will appreciate that such rolls have a tendency to bow during use thereof. Although crown compensating rolls are used to compensate for such bowing, there still exists a tendency for a doctor to bow slightly when the doctor blade is pressed against the external surface of a press roll.
Also, in the case of a doctor in a dryer section, such drying cylinders tend to bow and such bowing cannot be compensated for as in the case of press rolls.
Accordingly, not only is it necessary that the bearing apparatus accommodate rotational and axial movement of the doctor, but also, the bearing apparatus must accommodate the relative bowing of the doctor blade during use thereof. Such bowing of the doctor blade effectively means that the rotational axis of a doctor journal becomes angularly disposed relative to the longitudinal axis of the bearing housing.
In the past, a bearing for an oscillating doctor has included a rubber bushing which stretched and compressed to compensate for the aforementioned angular movement of the doctor relative to the longitudinal axis of the housing.
However, such rubber bushings have required frequent replacement, especially in view of the hostile environment in which such bearings are disposed.
In operation of a papermaking machine, it is not unusual for the equipment, including the doctor bearings, to be hosed with a chemical solution in order to remove contaminants from the papermaking machine. Such chemical solutions have an adverse effect on the rubber bushings and corrosion sensitive materials of the prior art bearings, thus tending to cause their early failure.
The present invention provides a bearing apparatus of unique construction which positively accommodates the angular movement of the doctor journal relative to the housing without the need of compressing the bearing material. Also, the present invention enables convenient replacement of the bearing in the unlikely event of the failure of such bearing.
Therefore, it is a primary objective of the present invention to provide a bearing apparatus which overcomes the aforementioned inadequacies of the prior art bearings for doctor journals, and which provides a significant contribution to the art of doctoring a web.
Another object of the present invention is the provision of a bearing apparatus which permits angular movement of a sleeve within a bearing ring but which inhibits axial movement of the sleeve relative to the bearing ring.
Another objective of the present invention is the provision of a bearing apparatus having a bearing ring which defines a split such that expansion of the diameter of the ring is permitted while the ring is slipped over an external face of a sleeve prior to sliding the combination of the sleeve and the ring axially within a cylindrical bore of a housing.
Another object of the present invention is the provision of a bearing apparatus having a bearing ring which defines a split such that the split accommodates any relative thermal expansion between a sleeve, a housing and the bearing ring.
Another object of the present invention is the provision of a bearing apparatus having a bearing ring which contains TEFLON. TEFLON is a registered trademark of E. I. DuPont De Nemours & Company of Wilmington, Del.
Another object of the present invention is the provision of a bearing apparatus which permits the doctor journal, together with the sleeve and ring, to oscillate axially relative to a housing.
Another object of the present invention is the provision of a bearing apparatus in which the sleeve defines an external face having a spherical surface with a center of curvature on the longitudinal axis of a cylindrical bore defined by a housing such that rotation of the sleeve in any direction within a bearing ring is permitted while the inner surface of the bearing ring captivates the sleeve when the bearing ring is disposed within the cylindrical bore.
Another object of the present invention is the provision of a bearing apparatus in which the external face of a sleeve has a surface roughness which is greater than the surface roughness of a cylindrical bore of the housing such that the sleeve and ring in combination oscillate axially within the cylindrical bore while relative axial movement between the external face and the inner surface of the ring is inhibited.
Another object of the present invention is the provision of a bearing apparatus having a bearing ring which captivates a doctor journal sleeve such that the need for any bearing seal or the like is avoided.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.